Coexistence of multiple charge-density waves and superconductivity in SrPt2As2 revealed by 75As-NMR/NQR and 195Pt-NMR

TL;DR

This study reveals the coexistence of two distinct charge density wave orders and superconductivity in SrPt2As2, showing that superconductivity is robust and likely in a spin-singlet s-wave state despite the presence of CDWs.

Contribution

The paper provides the first detailed NMR/NQR investigation of multiple CDWs coexisting with superconductivity in SrPt2As2, identifying two separate CDW transitions and confirming the s-wave nature of the superconducting gap.

Findings

Two distinct CDW orders at 410 K and 255 K in different layers.

Superconductivity exhibits a Hebel-Slichter peak and exponential decay below Tc.

Superconductivity is in a spin-singlet s-wave state, robust against CDWs.

Abstract

The relationship between charge density wave (CDW) orders and superconductivity in arsenide superconductor SrPt$_2$As$_2$ with $T_c$ = 5.2 K which crystallizes in the CaBe$_2$Ge$_2$-type structure was studied by $^{75}$As nuclear magnetic resonance (NMR) measurements up to 520 K, and $^{75}$As nuclear quadrupole resonance (NQR) and $^{195}$Pt-NMR measurements down to 1.5 K. At high temperature, $^{75}$As-NMR spectrum and nuclear spin relaxation rate ($1/T_1$) have revealed two distinct CDW orders, one realized in the As-Pt-As layer below $T_{\rm CDW}^{\rm As(1)}$ $=$ 410 K and the other in the Pt-As-Pt layer below $T_{\rm CDW}^{\rm As(2)}$ $=$ 255 K. The $1/T_1$ measured by $^{75}$As-NQR shows a clear Hebel-Slichter peak just below $T_c$ and decreases exponentially well below $T_c$. Concomitantly, $^{195}$Pt Knight shift decreases below $T_c$. Our results indicate that superconductivity in SrPt$_2$As$_2$ is in the spin-singlet state with an $s$-wave gap and is robust under the two distinct CDW orders in different layers.